1. Field of the Invention
The present invention relates to a process and an apparatus for treating a water containing chlorinated organic compounds. Particularly, it relates to a treatment process and an apparatus for purifying groundwater, wastewater or the like containing aliphatic chlorinated organic compounds such as trichloroethylene, dichloroethylene, vinyl chloride, or aromatic chlorinated organic compounds such as chlorobenzene.
2. Description of Related Art
In recent years, there have been cases that aliphatic chlorinated organic compounds such as trichloroethylene, which are often used as cleaning agents in semiconductor factories or metal processing factories, leak from storage facilities or from wastewater, resulting contamination of soil and groundwater. Such leakage poses serious environmental problems. Contaminated groundwater has been conventionally treated mainly by pumping the contaminated groundwater, stripping the contaminant by air in an aeration column and then releasing it into the atmosphere or adsorbing it into activated carbon. If the contaminant is directly released into the atmosphere, treatment can be accomplished at low cost involving only aeration costs. However, this is an insufficient treatment process since it merely transfers the contaminant from water to the atmosphere thus giving rise to air pollution. If the contaminant is adsorbed into activated carbon, however, regeneration costs are incurred for regenerating spent activated carbon, and recovered chlorinated organic compounds must be disposed of. Wastewater containing chlorinated organic compounds have also been treated in the same manner or combined with other wastewater and treated by an activated sludge process or similar treatment process using an aerobic organism. However, problems also exist in these treatments since the compounds concerned are readily vaporizable with the result that they may be immediately diffused into the air by aeration.
Various techniques for biologically degrading such chlorinated organic compounds by biologically treating them with methanotrophs, phenol-degrading bacteria, toluene-degrading bacteria or the like have been proposed, but no practically feasible technique has yet been established. For example, a treatment technique using a bioreactor containing a methanotroph immobilized in gel has been proposed (JPB No. 67314/94). However, degrading bacteria which have once degraded chlorinated organic compounds such as trichloroethylene (TCE) rapidly decrease their trichloroethylene degradation activity, and many problems still remain for achieving a continuous and stable treatment on a practical level.
A bioreactor system for biodegrading trichloroethylene with a methanotroph has also been proposed (MIPR Nos. N91-84, N92-63: Herbes, S. E., Palumbo, A. V., Strong-Gunderson, J. L., Donaldson, T. L., Sayler, G. S., Bienkowski, P. R., Bowman, J. L., and Tschantz, M. F., "Innovative Bioreactor Development for Methanotrophic Biodegradation of Trichloroethylene", report number AL/EQ-TR-1994-0007, January 1994).
As shown in FIG. 5, this bioreactor system 20 comprises a continuous stirred tank reactor 22, four plug-flow reactor columns 24 and a dewatering column 26. Methane and oxygen are supplied to the tank reactor 22 via a flow controller not shown and a methanotroph is cultivated in the tank reactor 22.
Then, a liquid containing the methanotroph is introduced into one of the reactor columns 24 from the tank reactor 22. This reactor column 24 is fed with trichloroethylene. In this reactor column 24, the methanotroph biodegrades trichloroethylene. A formate is supplied between the second and third stage reactor columns.
The liquid having passed through the reactor columns 24 is reintroduced into the tank reactor 22.
The liquid in the tank reactor 22 is introduced to the dewatering column 26. The dewatering column 26 contains a porous metal filter covered with a TEFLON.RTM. layer having a pore diameter of 0.22 .mu.m. Wastewater having permeated the metal filter is discharged, while the retained methanotroph or the like is reintroduced into the tank reactor 22.
With this bioreactor system 20, however, a gas such as methane supplied to the tank reactor 22 is partially dissolved in the liquid and discharged with effluent through the dewatering column 26. Namely, it has the disadvantage that the gas supplied to the tank reactor 22 is partially wasted. Moreover, it was difficult to reduce the size of the system because the tank reactor 22 and the dewatering column 26 should be separately provided. SUMMARY OF THE INVENTION
A first aspect of the present invention relates to a process for treating a water containing chlorinated organic compounds with a microorganism, wherein the microorganism is introduced from a degradation tank to a separation tank and an energy source is supplied to the microorganism separated in the separation tank to reduce the loss of energy source such as methane or propane discharged from the separation tank.
A second aspect of the present invention relates to an apparatus for treating a water containing organic compounds such as chlorinated organic compounds, which has a structure capable of continuously introducing water to be treated through a degradation tank, a separation tank and a reactivation tank. Thus, loss of an energy source such as methane or propane discharged from the separation tank can be reduced.
A third aspect of the present invention relates to an apparatus for treating a water containing organic compounds such as chlorinated organic compounds, wherein the microorganism can be cultivated in a separation tank so that the need for a reactivation tank is obviated and the overall size of the apparatus can be reduced. The apparatus of the present invention is not limited to use in the degradation of chlorinated organic compounds, but can also be used to degrade other organic compounds.
Accordingly, the first aspect of the present invention provides a process for treating a water containing chlorinated organic compounds, comprising the steps of treating a water containing chlorinated organic compounds with a microorganism capable of degrading chlorinated organic compounds in a degradation tank, introducing thus treated water to a separation tank, separating a composition containing said microorganism from said treated water in said separation tank to afford a clarified water substantially free from said microorganism, and then supplying an energy source for said microorganism.
Preferably, the step of supplying an energy source for said microorganism takes place in said separation tank. Preferably, the process comprises the step of introducing said microorganism in said separation tank to said degradation tank. Also preferably, the process comprises a circulation step for extracting an upper gas accumulating at the upper portion of said separation tank and introducing it into the lower portion of said separation tank, and said energy source is supplied in said circulation step.
On the other hand, the process preferably comprises the step of introducing said composition to a reactivation tank where said supplying step takes place. Also it preferably comprises the step of introducing said microorganism in said reactivation tank to said degradation tank.
Preferably, said microorganism is a methanotroph, a propane-oxidizing bacterium, a toluene-oxidizing bacterium, a phenol-oxidizing bacterium, an ammonia-oxidizing bacterium or a bacterium capable of degrading chlorinated aryls.
More preferably, said microorganism is a methanotroph. Preferably, a mixed gas containing methane and oxygen is supplied to said methanotroph in an aqueous solution in said supplying step, and the dissolved oxygen concentration in said aqueous solution is 20-400 .mu.g/l. Namely, the dissolved oxygen concentration in the reactivation tank is preferably 20-400 .mu.g/l when the methanotroph is cultivated in the reactivation tank, or the dissolved oxygen concentration in the separation tank is preferably 20-400 .mu.g/l when the methanotroph is cultivated in the separation tank.
Preferably, a microorganism contained in enrichment cultures is used in said water-treating step. Preferably, said degradation tank has an inlet and an outlet, said water to be treated is introduced from said inlet of said degradation tank and the concentration of chlorinated organic compounds gradually decreases from said inlet to said outlet of said degradation tank.
The second aspect of the present invention provides an apparatus for treating a water containing organic compounds, comprising a degradation tank adapted to treat water containing organic compounds with a microorganism capable of degrading organic compounds, a separation tank adapted to separate a composition containing said microorganism from thus treated water to afford a clarified water substantially free from said microorganism, a reactivation tank adapted to activate or proliferate said microorganism, a feed line means connected to said reactivation tank and adapted to supply an energy source to said microorganism in said reactivation tank, a first line means for introducing said microorganism in said degradation tank to said separation tank, and a second line means for introducing said separated microorganism in said separation tank to said reactivation tank.
Preferably, the apparatus has a recycle line means for introducing the microorganism in said reactivation tank to said degradation tank. Said separation tank preferably has hollow fiber membranes or a filter therein. The apparatus preferably has a circulation line means for extracting an upper gas accumulating at the upper portion of said separation tank and introducing it into the lower portion of said separation tank. The apparatus preferably has a gas line adapted to introduce a gas into said circulation line means.
The third aspect of the present invention provides an apparatus for treating a water containing organic compounds, comprising a degradation tank adapted to treat water containing organic compounds with a microorganism capable of degrading organic compounds, a separation tank adapted to separate a composition containing said microorganism from thus treated water to afford a clarified water substantially free from said microorganism, a first line means for connecting said degradation tank to said separation tank, and a feed line means connected to said separation tank and adapted to supply an energy source to said microorganism in said separation tank.
Preferably, the apparatus has a circulation line adapted to extract an upper gas accumulating at the upper portion of said separation tank and introduce it into the lower portion of said separation tank in order to allow it to circulate, and said feed line means has a gas line means connected to said circulation line and adapted to introduce a gaseous energy source. Also, it preferably has a recycle line means for introducing said microorganism in said separation tank to said degradation tank.
Said separation tank preferably has hollow fiber membranes or a filter therein. Said degradation tank preferably has one vessel.